河南方城大庄铌-稀土矿床碱性正长岩成矿机理研究

【研究目的】河南方城大庄是新探明的中型铌-稀土矿床（Nb₂O₃资源量16245 t；伴生TRE₂O₃资源量30147 t），矿体主要赋存在碱性正长岩内。【研究方法】本文在野外地质调查基础上，对含矿碱性正长岩与无矿碱性正长岩开展了岩石学、岩相学和地球化学的对比研究。【研究结果】研究结果表明，含矿与无矿碱性正长岩均富碱、富铝，为典型的A型花岗岩，两类岩石的碱金属含量无明显差别，但（Na₂O+K₂O）/CaO、FeO^*/MgO、K₂O/MgO等参数明显不同。含矿碱性正长岩高场强元素Nb、Ta、Ce、U、Th、Zr、Y明显富集，Ba、Sr、P、Eu明显亏损；无矿碱性正长岩大离子亲石元素Rb、高场强元素Nb、Ta、Y和Th元素明显富集，而Ba、U、Sr、P、Ti和重稀土元素明显亏损，但亏损程度低于含矿碱性正长岩。【结论】方城大庄含矿碱性正长岩不是无矿碱性正长岩热液蚀变（钠长石化）的结果，二者应是同一岩浆体系不同演化阶段溶体固结的产物，含矿碱性正长岩的分异演化程度明显高于无矿化的碱性正长岩。方城大庄稀有稀土元素的富集与岩浆高演化、分异过程密切相关。这一研究可为区域找矿勘查提供一定的地质依据。创新点：岩石学和地球化学对比研究显示大庄Nb-REE矿中含矿碱性正长岩具有比无矿岩体更高的演化程度，表明成矿元素的富集与岩浆高分异演化密切相关，为找矿勘查提供了一定的岩石学证据。

Metallogenic mechanism of alkalinesyenite in Dazhuang Nb-REE deposit, Fangcheng, Henan Province

This paper is the result of mineral exploration engineering.Objective] Dazhuang deposit is a newly discovered medium-sized Nb-REE deposit (Nb₂O₃=16245t; Associated TRE₂O₃=30147 t) in Fangcheng, Henan Province and its ore body occurs within alkaline syenite.Methods] In this paper, the authors compared the differences between ore-bearing and barren alkaline syenites in terms of petrology, petrography and geochemistry based on detailed field observation.Results] The results show that both ore-bearing and barren alkaline syenites belong to typical A-type granite which is rich in alkaline and aluminium and there is no significant differences in alkali metal contents between them, whereas the ratios of (Na₂O+K₂O)/CaO, FeO^*/MgO, K₂O/MgO are obviously different. Moreover, the ore-bearing alkaline syenite has high contents of high field strength elements such as Nb, Ta, Ce, U, Th, Zr and Y, but is depleted in Ba, Sr, P and Eu. The barren alkaline syenite displays high content of large ion lithophile elements of Rb and some high field strength elements such as Nb, Ta, Y and is depleted in Ba, U, Sr, P, Ti and heavy rare earth elements however, its depleted degree is lower than that of ore-bearing alkaline syenite.Conclusions] The comprehensive analysis implies that the ore-bearing alkaline syenite in Dazhuang deposit was not the product generated by hydrothermal alteration (albitization) of barren alkaline syenite, but formed from the same magmatic system at different evolution stages. The fractionation degree of the ore-bearing alkaline syenite is obviously higher than that of barren syenite and the enrichment of rare elements and rare earth elements in Fangcheng Dazhuang deposit is closely related to the high evolution process of A-type magma. These results may provide some petrological evidences for the REE prospecting in Fangcheng district.Highlights: Conclude that the ore enrichment mechanism is closely related to the high fractionation process of magmatic system. These results provide some petrological evidences for ore prospecting in Fangcheng district.